'If' for
things that are always or usually true

Examples:

"If I do well in my exams, I feel happy. If I don't, I feel sad."

"If you breathe out on a very cold day you can see your breath steam."

"If you smell smoke you should phone 999."

Grammar:

In the first example both the 'if' part of the sentence and the other part of the
sentence use the present simple tense.
In the second two examples there is present simple tense in the 'if' part of the sentence,
and then a modal verb followed by an infinitive verb in the other part.

'If' for promises and negotiations

Examples

"If you scratch my back, I'll scratch yours." (Meaning: If you help me, I'll
help you.)

"If you pay in cash I'll give you 5% off."

Grammar:

The 'if' part of the sentence has a present simple tense verb and the other part of the
sentence has a future tense verb.

'If' and missing things or information

Examples in the present:

"If I had an umbrella, I wouldn't be wet." (but I don't have an umbrella now,
so I am wet.)

"If I knew where he was, I would tell you." (but I don't know where he is now,
so I can't tell you.)

"If I knew what she wanted, I would give it to her." (but I don't know what
she wants so I can't give it to her.)

"What would you do if you won the Mark Six?"
"If I won the Mark Six, I would travel all over the world." (but I haven't won
the Mark Six, so I can't.)

Grammar:

The 'if' part of the sentence uses the past simple tense. The other part of the
sentence uses 'would' and an infinitive verb. Would is often shortened to _'d; e.g.
"If I won the Mark 6, I'd travel all over the world."

Examples in the past:

"If I had taken an umbrella, I would not have got wet." (but I didn't, so I
did get wet.)

"If I had known where she was, I would have told you." (but I didn't know
where she was, so I couldn't tell you.)

If I had known what she wanted, I would have given it to her." (but I didn't know
what she wanted, so I couldn't give it to her.)

Grammar:

The 'if' part of the sentence uses the past perfect tense. The other part of the
sentence uses 'would' and the present perfect tense.

IF
by Rudyard Kipling

If you can keep your head when all about you
Are losing theirs and blaming it on you;
If you can trust yourself when all men doubt you
But make allowance for their doubting too;
If you can wait and not be tired by waiting;
Or being lied about, don't deal in lies,
Or, being hated, don't give way to hating;
And yet don't look too good, nor talk too wise;

If you can dreamand not make dreams your master;
If you can thinkand not make thoughts your aim;
If you can meet with triumph and disaster
And treat those two impostors just the same;
If you can bear to hear the truth you've spoken
Twisted by knaves to make a trap for fools,
Or watch the things you gave your life to, broken,
And stoop and build 'em up with worn-out tools;

If you can make one heap of all your winnings
And risk it on one turn of pitch-and-toss,
And lose, and start again at your beginnings
And never breathe a word about your loss;
If you can force your heart and nerve and sinew
To serve your turn long after they are gone,
And so hold on when there is nothing in you
Except the Will which says to them: Hold on;

If you can talk with crowds and keep your virtue,
Or walk with kings--nor lose the common touch;
If neither foes nor loving friends can hurt you;
If all men count with you, but none too much;
If you can fill the unforgiving minute
With sixty-seconds' worth of distance run
Yours is the Earth and everything that's in it,
Andwhich is moreyou'll be a Man, my son!

Grammar:

'If' for things that are
always or usually true:"If you can talk with crowds and keep your virtue,... yours is the
earth..."
These lines, and most of the lines in the poem, give rules that are generally or usually
true about life. They use 'can' plus an infinitive verb or present tense verbs.

'If' for promises:"If you can fill the unforgiving minute... you'll
be a Man, my son!"'you'll' = you will - a promise for the future. It means that if you follow the rules
in the poem you will become a mature man.